The invention provides novel 7,8-dihydro-imidazo[1,2-a]pyrazolo[4,3-e]pyrimidin-4-one compounds and 7,8,9-trihydro-[1H or 2H]-pyrimido[1,2-a]pyrazolo[4,3-e]pyrimidin-4(5H)-one compounds, substituted at the 1 or 2 position with C2-9 alkyl, C3-9 cycloalkyl, heteroarylalkyl, or substituted arylalkyl, in free, salt or prodrug form, processes for their production, their use as pharmaceuticals, particularly as PDE1 inhibitors, and pharmaceutical compositions comprising them.